The invention relates to an adjustable steering column for a motor vehicle with a setting part displaceable in at least one setting direction for setting the position of the steering column, a holding part nondisplaceable in this setting direction, a securement device, in the opened state of which the setting part is displaceable with respect to the holding part for setting the position of the steering column and, in the closed stage of which, the setting part is secured in place by the securement device, and a crash-blocking means, by which in the event of a crash an additional holding force against a dislocation of the setting part with respect to the holding part can be exerted and which comprises a clamping wedge, which, in the event of a crash, can be slid into a gap between the setting part and the holding part and be wedged in it.
Adjustable steering columns are known in different embodiments. The length of the steering column as well as also its inclination or height can conventionally be changed in the open state of a securement means. To fix the set position in the closed state of the securement means, intersecting disk packs may for example be provided of which the one is secured on the shell unit receiving the steering spindle and the other is secured on a support unit connected with the chassis. The intersecting disk packs are penetrated by a clamp bolt and mutually clamped by actuating a clamping lever. To permit displacement, in the disk packs as well as in the shell unit and in the support unit elongated holes are disposed through which the clamp bolt penetrates, the elongated holes intersecting one another for the axial adjustment of the steering column and for the height adjustment of the steering column. Such an adjustable steering column is disclosed for example in EP 0 802 104 B1.
A further adjustable steering column with a securement device implemented in the manner of a lamella stack is disclosed for example in U.S. Pat. No. 6,581,965 B2.
Known are further adjustable steering columns, in which the securement device comprises toothed parts, which, in the closed state of the securement device, mesh with one another and consequently block the axial displacement and height displacement of the steering column. Such a steering column is for example disclosed in EP 0 836 981 B1. In the event of a crash, in spite of the very high forces occurring, relative movements in the displacement mechanism of the steering column should as much as possible be excluded, inter alia in order for the air bag to be able to unfold its full effectiveness as an impact protection for the driver. The securement devices serving to secure the steering column in normal operation are conventionally not suited to absorb these high forces in the event of a crash, since their implementation would otherwise be highly complex and expensive and would require a great deal of installation space. For that reason steering columns have already been proposed which include additional crash blocking means, which, in the event of a crash exert an additional holding force against a dislocation of the shell unit with respect to the support unit. EP 1 044 127 B1 discloses for example to develop at the instance of impact of the motor vehicle onto a hindrance a positive locking connection between the shell unit and a chassis-stationary support unit through pyrotechnical means. Of disadvantage is the relatively complex implementation of such a steering column, wherein a sensor system for the acquisition of the impact and for triggering the pyrotechnical means is also required.
The adjustable steering column of DE 195 06 210 C1 comprises a blocking element with a blade edge which can be pressed onto a clamp flange during the closing of the securement device. In the event of a crash the blade edge of this blocking element digs into the material of the clamp flange in order to yield as much as possible a positive locking of the shell unit of the steering column with the vehicle body-stationary holding unit. Of disadvantage in such unit is that the reliable pressing-in of the blade edge into the material of the clamp flange, and consequently the positive locking, in continuous operation cannot be ensured with certainty in the even of a crash. Moreover, an increased closing force is required for closing the securement device.
An adjustable steering column of the type described in the introduction is disclosed in DE 196 17 561 C1. Herein a clamping wedge is displaceably supported on a shell tube rotatably supported on an axially displaceable part of the steering spindle, which wedge is acted upon by a spring into its passive position in a direction displaced with respect to the steering wheel. In the event of a crash, the acceleration force acting onto the clamping wedge effects a displacement of the clamping wedge acting independently of the securement device against the force of the spring, wherein the clamping wedge is driven into a gap between the shell tube and an axially nondisplaceable section of the steering spindle and consequently blocks the dislocation of the shell tube relative to the axially nondisplaceable steering spindle and thus also relative to a chassis-stationary holding part of the steering column. Such an implementation does not sufficiently ensure that the crash blocking means becomes reliably effective in the event of a crash. In addition to a clamping wedge, DE 196 17 561 C1 describes arresting parts also developed in different form, such as for example in the form of a retaining ball or pivot jaw. A sensor-controlled displacement device for conveying the arresting parts independent of the securement device into its effective position is also cited.